The explosion of high bandwidth applications over Internet has fuelled the deployment of broadband optical transport networks. Some of the key applications driving the bandwidth growth include residential services like IP-TV, Video on Demand and high speed Internet and enterprise services like high-bandwidth leased lines and Virtual Private Networks (VPN). The falling prices of mobile calls and broadband services coupled with an increase in the tele-density and the uptake of broadband and 3G services have put pressure on service providers to build high capacity transport networks at dramatically lower cost per bit. In the converged telecom scenario, the service providers are looking for network access architecture that would not only provide scalable high bandwidth but at the same time offer flexibility in provisioning, Service Level Agreement (SLA) with Quality of Service (QoS) guarantees for real time traffic and protection and restoration capability, efficient multicast and network synchronization services for wireless access. Toward this goal, several new architectures have emerged.
Traditionally, SDH has been the sole transport network and carried all of the telecommunication service provider's traffic, including voice and data. One of the advantages of SDH based transport network is their 50 msec protection and restoration capability. With a shift towards Internet Protocol (IP) traffic, SDH based transport networks have proved inefficient. This has resulted in a paradigm shift towards packet based transport. With an increase of packet traffic, the SDH networks have evolved to Next Generation (NG) SDH where Ethernet frames are encapsulated in SDH payloads. The NG-SDH protocol defines mapping of SDH payload to SDH channels which are either higher order or lower order virtual containers (VC). All other features like 50 msec protection and restoration are retained. However, SDH network only supports point-to-point circuits. To provide the packet multiplexing efficiencies and any-to-any connectivity paradigm required by the data traffic, SDH devices have been enhanced by integrating the packet aggregation capabilities.
Carrier Ethernet based transport networks have emerged as the dominant choice for an efficient packet transport networks. Carrier Ethernet networks offer several value propositions like lower per-user provisioning cost, efficient and flexible transport, wide range of bandwidth etc. Ethernet based services like Virtual Private LAN Service (VPLS) are also becoming attractive service offerings. However, Ethernet in its native mode suffers from scalability, protection and restoration, traffic engineering and Quality of Service. To address these issues, Provider Bridge (IEEE 802.1ad), Provider Backbone Bridging (PBB) (IEEE 802.1ah) and PBB with Traffic Engineering (PBB-TE) (IEEE 802.1Qay) have been introduced. Ethernet has also been enhanced with Operations, Maintenance and Administration (OAM) functionality: CFM-OAM (IEEE 802.1ag) and EFM-OAM (IEEE 802.3ah). Ethernet based services can also be provided using hybrid Layer 2/Layer 3 architecture using Multiprotocol Label Switching (MPLS) and a variant of MPLS called Transport-MPLS (T-MPLS).
While PBB has attempted to address many carrier class features, protection and restoration remains an issue. IEEE 802.1d Spanning Tree Protocol (STP) is one of the first attempts to address protection in Ethernet based networks. Later this was enhanced with Rapid Spanning Tree (RSTP) (IEEE 802.1w). Some of the other attempts to address protection and restoration in Ethernet networks include Ethernet Automatic Protection Switching (EAPS) RFC 3619.
The present invention attempts to address this issue of protection and restoration in Ethernet based transport networks for both unicast and multicast traffic. Unlike the method given in
[Redundant Trees for Preplanned Recovery in Arbitrary Vertex-Redundant or Edge-Redundant Graphs
Muriel M'edard and et. al. IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 7 NO. 5, OCTOBER 1999], our method is a systematic method. Also our method is not greedy. Moreover our method does not give singularity of work tree and a singularity of protect tree.
The available protection mechanisms for multicast traffic are not efficient. For example, a 1:1 or 1+1 backup tree is maintained to carry the affected multicast traffic. This mechanism sets up a backup tree at the time of connection establishment thus, leading to delay in setting up the traffic because finding such a tree at the time of connection establishment will take time proportional to the network complexity. Management of such a network is not simple and easy.